Evacuated villagers from locations near the summit of Mount Agung, an active volcano which is showing increased seismic activity, relax in a temporary shelter in Klungkung, on the resort island of Bali, Indonesia Sept 22, 2017 in this photo taken by Antara Foto. Antara Foto via Reuters

Mount Agung, an active volcano located on the resort island of Bali that has been placed on alert level 3 following recent seismic activity, is seen from Mataram on nearby Lombok island, Indonesia Sept 21, 2017, in this photo taken by Antara Foto. Antara Foto via Reuters

A man takes a picture of a map of the danger zones around Mount Agung, a day after the volcano's alert status was raised to the highest level, at a government monitoring station and observatory in Rendang, on the resort island of Bali, Indonesia Sept 23, 2017. Reuters

Nearly 35,000 people have been evacuated from near a volcano on the Indonesian holiday island of Bali that officials say is becoming more active and could erupt soon.

Authorities imposed a 12-km exclusion zone around the crater of Mount Agung, as increasing volcanic activity on Sunday sent strong tremors through areas in the eastern part of the one of the world's most popular tourist destinations.

Officials urged the public to remain calm amid false reports and videos circulating online of an eruption.

Mount Agung, an active volcano located on the resort island of Bali that has been placed on alert level 3 following recent seismic activity, is seen from Mataram on nearby Lombok island, Indonesia Sept 21, 2017, in this photo taken by Antara Foto. Antara Foto via Reuters

"The latest analysis indicates that Mount Agung's seismic energy is increasing and has the potential to erupt," the National Vulcanology Center said in a statement.

"However, no one can predict exactly when there will be an eruption," it added.

Flights at Bali's international airport were operating normally on Sunday as were tourist spots across the rest of the island.

Thousands of evacuees were being housed in makeshift shelters including town halls and school gyms and tents in villages around the volcano, and authorities expect the numbers to climb.

"The biggest challenge is we can't predict the number of evacuees," said Putu Widiada, head of the local disaster management agency in Klungkung district.

"If the number of evacuees exceeds our maximum capacity, we have asked that every public hall in the district be prepared to become evacuation camps."

A man takes a picture of a map of the danger zones around Mount Agung, a day after the volcano's alert status was raised to the highest level, at a government monitoring station and observatory in Rendang, on the resort island of Bali, Indonesia Sept 23, 2017. Reuters

The shelters were well stocked with food, water, blankets and tents.

The National Disaster Management Agency has sent food and logistical supplies to the area, while also calling for public donations.

Many residents are still making daytime trips to their homes and life is largely continuing as normal in the area.

Indonesia has nearly 130 active volcanoes, more than any other country. Many Indonesians live near volcanoes because lava flows can make the surrounding soil and land fertile for farming.